1. Field of the Invention
The invention relates to magnetic compasses and more particularly to a magnetic compass with both a digital and an analog readout.
2. Description of the Prior Art
There is a need for a dual readout (digital and analog) magnetic compass that displays both forms of readout in a single housing without interference between the electronic circuitry associated with the digital readout and the compass magnet without excessive cost and is also capable of being operated in a remote readout mode. Dual readout magnetic compasses are well known. U.S. Pat. No. 4,139,951 discloses a dual readout compass. However, it utilizes a rotating conductor such as a coil, which makes it significantly more expensive than compasses utilizing a simple permanent magnet compass card or magnetic needle.
Digital readout compass displays, too, are known in the art. See, U.S. Pat. Nos. 3,888,016, 4,075,619 and 4,139,951. However, the familiar permanent magnet compass, when combined with a digital readout, is subject to interference between the magnet and the electromagnetic fields generated by the digital readout electronics. The digital readout employs electronic logical circuitry. This circuitry generates electromagnetic fields. When the circuitry is in close proximity to the magnetic needle of the compass, the stray magnetic fields generated by the circuitry affect the magnet, thus preventing it from accurately responding to the earth's magnetic field. The problem may be particularly troublesome when compass headings of fractions of a degree are sought or when the compass is placed in the instrument panel of, say, an aircraft, where it is surrounded by numerous gauges and instruments employing electromagnets to operate dials and counters. The interference between such instruments and the magnetic compass may be reduced by isolating the compass, as by locating the compass on a remote part of the aircraft, say, a wingtip, and employing a remote readout device to display the compass heading in the cockpit. In such a configuration, there still remains interference between the magnetic compass and the magnetic fields generated by the remote readout electronics. The interference between the compass magnet and the digital readout electronics may be reduced by shielding the circuitry with a Faraday type shield.
It is a principal object of this invention to provide a magnetic compass with dual readouts capable of displaying headings in analog and digital forms in a single housing with the capability for remote display of the digital reading. The principle of dual readout allows a continuous compass capability in all weather conditions as well as operation in night and daytime lighting conditions.
A second object of this invention is to provide a dual readout magnetic compass with the capability of measuring the inclination or slope of the ground upon which the instrument is in use and providing dual readout of the inclination in analog and digital form.
A third object of the invention is to provide a magnetic compass with digital readout that is not susceptible to distortion of the magnetic heading by electromagnetic influence of the electronic circuitry associated with the digital readout.
A fourth object of the invention is to provide an analog electronic readout of a magnetic compass by use of an analog optically encoded disk viewed by an electronic sensor such that the output voltage of the sensor is directly related to the heading.
A fifth object of the invention is to provide an improved magnetic compass that provides dual readout in a compact, inexpensive instrument.